1. Description of the Prior Art
Perforating guns have long been employed to achieve the perforation of a well casing and an adjacent production formation. Originally, such perforating guns were lowered into the casing to the desired location on a wire line and then electrically activated to effect their discharge. More recently, perforating guns have been conveyed on the bottom of a tool string having an uninterrupted bore through which a detonating bar could be dropped to effect the firing of the gun, or in which a fluid pressure could be developed to effect a fluid pressure actuated detonation of a perforating gun. The tubing conveyed perforating gun has the advantage that other operations, such as chemical treatment, washing and/or gravel packing of the perforations and the production screen, can be accomplished with a single trip of the tool string into the well. See for example U.S. Pat. No. 3,987,854 (Callihan, et al).
It has been previously suggested in the prior art that production tubing be utilized as the tool string on which the perforating gun is inserted in the well. In such case, it often becomes desirable to disconnect the perforating gun after the perforating operation has been performed so that the subsequent movements of the tool string to effect the positioning of the screen adjacent to the perforations and to effect the chemical treatment, washing and/or gravel packing of the perforations may be conveniently accomplished without requiring the movement of the additional weight of the discharged perforating gun. It is therefore desirable to provide an economical, yet reliable apparatus for effecting the release of the perforating gun from the tool string.
The release of a tubing conveyed perforating gun has heretofore been disclosed in the prior art. See for example U.S. Pat. No. 3,706,344 (Vann) and U.S. Pat. No. 4,040,482 (Vann) and earlier references. Such prior art references, however, contemplate the severance of a perforating gun from the tool string by a tubing cutter or a wire line operated latch releasing mechanism. Obviously, the employment of a tubing cutter or any wire line disconnecting device necessitates the introduction of substantial delay due solely to the operation of separating the perforating gun from the tool string.